Hot choco­late and sou­venir photos of a lu­nar eclipse

Wiarton Echo - - NEWS - John Hly­nialuk

There is an “oh-so-close” lu­nar eclipse hap­pen­ing Feb. 10. Tech­ni­cally it is a miss, and even if the skies are per­fectly clear, the best we can hope for is a slight dark­en­ing of part of the Moon’s face at the prime time of 7:44 p.m. Even then, you might not no­tice any­thing un­less you know ex­actly what to look for. Here’s what you need to know if you’d like to try to see it.

Eclipses are caused by shad­ows. The Sun sends light out in all di­rec­tions and dur­ing a lu­nar eclipse, the Earth blocks the Sun’s light and the Earth’s shadow falls onto the full Moon. Things have to be lined up per­fectly, so eclipses don’t hap­pen ev­ery month – the most we get is seven a year, about half of each type. In 2017, we get two so­lar and two lu­nar eclipses, a bit fewer than av­er­age.

Of the four eclipses this year, only one is re­ally worth get­ting ex­cited about and that is the so­lar eclipse on Aug. 21. I have to ad­mit that I have been ex­cited about that one for more than a year now and at the time of writ­ing there are only 201 days, 14 hours, 30 min­utes, 3.556 sec­onds to go! (ap­prox­i­mately).

Lu­nar eclipses would hap­pen more often ex­cept the Moon’s or­bit around Earth is tilted and Earth’s shadow goes over or un­der the Moon most times. Se­condly, there are two parts to the Earth’s shadow that can cover the Moon, an eas­ily-seen dark cen­tral area, the um­bra, and a sur­round­ing penum­bra, but it al­lows most of the sun­light through and is barely de­tectable. A penum­bral eclipse is what we will get on Feb. 10.

The shadow of Earth ex­tends past the Earth and forms a dark cone stretch­ing out to a point about 1,400,000 kilo­me­tres away in space. That’s al­most four times as far as the Moon is from us, so at the Moon’s dis­tance, the shadow’s cross-sec­tion (a cir­cle) is still big, al­most three times as wide as the full Moon. For that rea­son, lu­nar eclipses last sev­eral hours and so­lar eclipses, with a much smaller Moon shadow – only a few hun­dred kilo­me­tres across – last only a few min­utes.

The shadow of Earth on Feb. 10 comes close but does not ac­tu­ally con­tact the um­bra (it gets 99 per cent of the way there). The sec­ond lu­nar eclipse this year, on Aug. 7, is a bit bet­ter but still only par­tial and worse yet, for the whole eclipse, the Moon is be­low our horizon – the best view will be in the Mid­dle East.

The one bit of good news for Feb. 10 is that it may be pos­si­ble to see a dark­en­ing due to the slightly darker, in­ner part of the penum­bral shadow. The outer penum­bra is just too faint to see when it touches the face of the Moon at 5:34 p.m. By 7:44 p.m, how­ever, a dark­en­ing on the up­per left edge of the Moon (about 10:30 on the clock) may be dis­cernible for per­haps 20 min­utes ei­ther side of the prime time. The only way to tell for sure is to take a pic­ture at 7:44 p.m. and com­pare it to an­other taken two hours later when the eclipse is over and the Moon is back to full bright­ness.

If it is clear Fri­day night, Feb. 10, the Fox Ob­ser­va­tory at the Out­door Ed­u­ca­tion Cen­tre near Oliphant will be open to the pub­lic and mem­bers of the Blue­wa­ter As­tro­nom­i­cal So­ci­ety will be there to show you the Moon. You are wel­come to take a sou­venir photo through the te­le­scope – even a cell phone will work. If the weather co­op­er­ates, there will be time to ob­serve the eclipse, take photos and have a hot choco­late to ward off the chill. Do join us.

The next good to­tal lu­nar eclipse vis­i­ble lo­cally hap­pens in two years on Jan. 21, 2019 but only a year from now, on Jan. 31, 2018, there is a good lu­nar eclipse vis­i­ble from the west coast of North Amer­ica if you are free to travel then (I hear the skiing is good out there at that time, too). Mark your cal­en­dars!

Check­wa­t­eras­tron­ for maps to the Fox Ob­ser­va­tory and other astron­omy in­for­ma­tion.

Di­a­gram from Wikipedia

At 7:44 p.m. dur­ing a penum­bral lu­nar eclipse Feb. 10, some dark­en­ing may be vis­i­ble on the up­per part of the full Moon.

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